Friction in Metal Cutting

FRICTION IN METAL CUTTIING Submitted by Arjyajyoti Goswami 02/PRD/2010

Submitted to Dr.. Reeta Wattal Dr W attal

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CAUSE OF FRICTION Microscopic examination examination shows that even the most carefully prepared ³flat´ metallic surfaces consist of numerous hills and valleys. When 2 surfaces are placed together, together, contact is established at the summit of only a few asperities in each surface

If a normal load is applied, yielding occurs at the tips of the contacting asperities, and the real area of contact A r increases until it is capable of









For vast majority of engineering applications this real area of contact Ar is only a small fraction of the apparent area of contact Aa and is given by Ar = Fn / y Fn is the normal force and  y is the yield pressure of the softer material The adhesion resulting from the intimate metallic contact of these asperities has been termed welding, and when sliding takes









Therefore the total frictional force is given by



Ff = f X Ar f is the shear strength of the softer material Combining the 2 equations it is found that coefficient of friction is independent of the apparent contact area , and since the ratio obtained is expected to be substantially constant for a given metal, the frictional force is proportional to the normal load.









RELEV REL EVANCE ANCE IN MET METAL AL CUTTING During metal cutting it is generally observed that the mean coefficient of friction between the chip and the tool can vary considerably and is affected by changes in cutting speed, rake angle etc This variation in friction is due to the very high normal pressures that exists at the chip tool interface.









Thus under the conditions of metal cutting the Ar reaches its maximum value and is constant throughout the machining operation

The frictional force is now independent of the normal force and the



















Presence of sticking friction was confirmed by the careful c areful investigation of the under surface of the chip on specimen where the cutting action was suddenly stopped

Through experiments it has been observed that the grinding marks on the tool were imprinted on the under surface of the chip









Effect of sticking and sliding region Under conditions of sticking friction , the mean angle of friction on the tool face will depend on the form of the normal stress distribution









ZOREV

assumed to the normal normal stress on the tool face face to be varying as Maximum normal stress occurs when x= l f therefore









So normal force Fn can be found as

Where aw is the width if the chip











So the final expression for frictional force is









It has been established that

Remains constant









results, obtained









NEW APPROACHES APPROACH ES TO ANAL ANALYSE YSE FRICTION FRICTI ON IN META METAL CUTTING CUT TING









A possibly improved friction model, currently being investigated,















Friction in Metal Cutting

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